The present invention relates generally to a mold structure for encapsulating a frangible sheet, such as glass, with a gasket. More particularly, the present invention relates to various improvements in the mold structure disclosed in U.S. Pat. No. 4,561,625 issued to William R. Weaver, assigned to the assignee of the present invention, and herein incorporated by reference. The gasket is typically formed of a polymeric material and is produced by a reaction injection molding process. The encapsulated window assembly can be shaped to constitute a vehicle windshield or backlight, for example.
Initially, windshield assemblies for vehicles were comprised of a plurality of elements including adhesive sealants applied around the marginal edges of the glass sheet, suitable mechanical fasteners such as metal clips, and exterior decorative trim strips disposed to cover the junction between the marginal edges of the glass sheet and the adjacent portion of the vehicle frame. Such window assemblies were costly, especially from a labor standpoint, since it was necessary to assemble the individual elements along the vehicle assembly line.
Subsequently, in an endeavor to improve the above window structure, unitary window assemblies of the type illustrated in U.S. Pat. No. 4,072,340 were developed. These assemblies include a sheet of glass, an adjacent frame, and a casing or gasket of molding material extending between the frame and the peripheral edge of the window to hold the sheet of glass and the frame together. The gasket was typically formed of a polyvinyl chloride material and was produced by an injection molding process.
However, due to the nature of the manufacturing process, glass sheets are typically produced with small irregularities or ripples in the surface thereof. Further, if a glass sheet is subsequently bent to have a curved cofiguration, it is difficult to produce a series of bent sheets each having the exact same dimensions. In a typical injection molding process for producing a polyvinyl chloride gasket, the polyvinyl chloride gasket material is typically injected at a relatively high pressure, generally ranging from 5,000 to 20,000 psi. Due to the high pressures involved, it is typically necessary that the mold structures have mold surfaces which engage the glass surface at a relatively high clamping pressure. Since the steel surfaces of the mold do not conform to the surface irregularity in the glass, and cannot be designed to do so, the high pressures often fracture the glass, particularly in the zones containing the irregularities.
Consequently, as disclosed in above-mentioned U.S. Pat. No. 4,561,625, W. R. Weaver developed a unique mold structure which can be utilized to form a polymeric gasket about a predetermined portion of a glass sheet by utilizing a reaction injection molding process. Since the pressures typically associated with a reaction injection molding process are less than those associated with the above described polyvinyl chloride injection molding process, the clamp tonnage required to secure and seal the glass sheet during the molding operation can be greatly reduced. Moreover, seals can be provided for resiliently supporting the glass sheet.
The mold structure of the Weaver patent includes a pair of cooperating mold sections having facing surfaces which define a glass receiving chamber for receiving a sheet of glass on which a gasket is to be formed. Seal means are provided in at least one of the facing surfaces of the glass sheet to resiliently support the glass sheet and prevent any metal-to-metal contact between the glass sheet and the mold sections inwardly of the seal means. The mold sections are provided with a gasket shaping portion which cooperates with the seal means and a predetermined peripheral portion of the glass sheet for defining a gasket forming cavity corresponding to the gasket to be formed on the sheet. In the Weaver patent, in order to precisely control the dimensions of the gasket forming cavity, at least a portion of the mold sections disposed outwardly of the gasket forming cavity are adapted to contact one another in metal-to-metal contact.